A toner for electrostatic image developing is generally manufactured through the following processes: the process for mixing binding resins and coloring agents with various additives added as needed; the process for melting and kneading the mixture using a kneading machine; the process for roughly grinding the kneaded and cooled mixture into a grain size of about several millimeters; the process for pulverizing the roughly ground material into a grain size of about several microns using the impact of collisions and the like; the process for classifying the pulverized material; the process for adding and mixing additives such as fluidizing agents and transcription auxiliaries to the material; and the process for removing bulky grains generated in the processes for mixing and the like. Recently, the grain size of toners has become increasingly finer so as to realize images of higher quality and the use of polyester resins as binding resin has increased so as to secure low-temperature fixity.
Because of the technical trend described above, a longer time is now required for the pulverizing process, which is originally a rate-controlling process, causing a fall in productivity. Pulverizers have been remodeled so as to improve grindability, but this method for improving productivity tends to increase the manufacturing cost owing to larger pulverizer size and higher energy consumption. The situation requires improvement in the grindability of the materials.
In order to solve these problems, there are methods for changing the component monomers of the binding resins or for reducing the molecular weight thereof. These methods, however, lower the softening point or glass-transition point of the toner although they improve the grindability thereof. As a result, the toner becomes apt to adhere to the interior of the pulverizer or classifier, or to the inside of the piping connecting them, or even to fuse therewith, affecting the manufacturing conditions. This also considerably affects the electrostatic properties or fixing properties of the toner. These methods realize good grindability at the sacrifice of much.
A material for improving grindability is known as another method. For example, a technique for making grindability compatible with fixing performance by using aromatic petroleum resins is described in Japanese Patent Kokai Hei 4-257868A. However, such aromatic petroleum resins as described in the official gazette are not satisfactory enough regarding color reproducibility, transparency, and the like when used as a part of the toner component because the material of these aromatic petroleum resins is made from a fraction which is a mixture of mainly styrene, vinyltoluene, α-methyl styrene, indene, diisobutylene, toluene, n-octane, xylene, p-ethyltoluene, dicyclopentadiene, β-methyl styrene, and naphthalene out of the decomposed oil fraction, a by-product from ethylene plants for producing ethylene, propylene and the like by steam cracking of petroleum, and as oligomers of which aromatic petroleum resins are generally colored.
A toner for electrostatic image developing which comprises at least a binding resin, a coloring agent, and a copolymerized resin containing at least one monomer based on styrene and one monomer based on indene is described in Japanese Patent Kokai Hei 11-65161A (corresponding to U.S. Pat. No. 5,972,547). However, as monomers based on indene are generally apt to get colored, the copolymerized resins thereof are also prone to get colored. Consequently, the toner disclosed in the official gazette is not satisfactory enough regarding color reproducibility and transparency. Besides, monomers based on indene must be refined to the extent of exceedingly high purity if the manufacture of non-colored copolymerized resins thereof is intended. Naturally, this requires special equipment, causing the problem of higher manufacturing cost.
Furthermore, a toner for electrostatic image developing which contains coloring agents, binding resins, and a copolymerized petroleum resin of aliphatic hydrocarbon with aromatic hydrocarbon having more than 9 carbon atoms is described in Japanese Patent Kokai Hei 11-72956 (corresponding to U.S. Pat. No. 5,958,642). Although the toner disclosed in the official gazette improves the grindability, heat preservability, and the dispersibility of the mold release agent, it does not realize satisfactory electrostatic properties.
An object of the present invention is to provide a toner additive which realizes an electrostatic image developing toner having good grindability in the pulverizing process and consequently making it possible to reduce the grain size easily in a short time, which causes no fusion with the equipment, and which does not affect the fundamental toner performances such as electrostatic performance, fixing performance, and coloring performance.
Another object of the present invention is to provide an electrostatic image developing toner and an electrostatic image developer, both containing said toner additive.